Any sample repo available for 2 apps authenticating users against 1 master app?

According to the Meteor Guide, it is possible to authenticate users against a different server:

But I have to admit that I have no clue how this is actually done, the docs are a bit sparse. So I am looking for a repo that showcases such a multi-app authentication scenario in practice.

Ideally, the solution should also support the useraccounts packages, mobile devices and social logins. But I would even be happy to get a kind of jump-start missing one or all of these requirements. Thx.